Chapter 5: Synaptic Transmission Flashcards
the specialized junction where one part of a neuron contacts and communicates with another neuron or cell type; where information transfer occurs
synapses
Direction of information flow in the nervous system is generally in one direction: ()
neuron to target cell
Otto Loewi discovered (1), later known as (2)
- Vagusstoff
- acetylcholine
Loewi studied action of the (1) in the frog heart system
vagus nerve
allow transfer of ionic current from one cell to the next
electrical synapses
the direct transfer of ionic current in electrical synapses occur at ()
gap junctions
due to current transfer at electrical synapses, a small electrical () occurs in the second cell
postsynaptic potential
gap junctions are composed of 2 () that meet and combine to form a continuous channel between 2 cells
connexons
1 connexon in formed by six ()
connexins
unlike most chemical synapses, electrical synapses are ()
bidirectional
In invertebrate species, electrical synapses are found between sensory and motor neurons: ()
escape reflexes
Bidirectional nature of electrical synapses allows () due to PSP from second cell
back current
Several PSPs cause AP in ()
postsynaptic neurons
(): several PSPs occurring simultaneously to excite a neuron (causes AP)
Synaptic integration
Presence of gap junction allows () of APs
synchronization
() – space between presynaptic terminal and postsynaptic dendrite
Synaptic cleft
Receptors are concentrated on postsynaptic side of dendrite: ()
postsynaptic density
() – site of neurotransmitter release
Active zone
Presynaptic element (usually an axon terminal) contains dozens of small membrane-enclosed spheres, each about 50 nm in diameter: (1); and about 100 nm in diameter (2).
- synaptic vesicles
- secretory granules/dense-core vesicles
CNS synapse type: axon to dendrite
axodendritic
CNS synapse type: axon to dendritic spine
axospinous
CNS synapse type: axon to cell body (soma)
axosomatic
CNS synapse type: axon to axon
axoaxonic
CNS synapse type: dendrite to dendrite
dendrodendritic
Two Categories of CNS Synaptic Membrane Differentiations
- Gray’s type I: asymmetrical
- Gray’s type II: symmetrical
CNS synapses with Gray’s type I membrane differentiations are usually ()
excitatory
CNS synapses with Gray’s type II membrane differentiations are usually ()
inhibitory
() – large amount of synapses connecting muscle fibers and motor neurons
Motor end plate
Neurotransmitter Categories (based on molecular structure)
- amino acids
- amines
- peptides
examples of amino acid neurotransmitters
glutamate, glycine, GABA
examples of amine neurotransmitters
dopamine, acetylcholine, histamine
examples of peptide neurotransmitters
dynorphin, enkephalins
because amines and amino acids are small organic molecules, they are stored in (1); on the other hand, peptide neurotransmitters are stored in (2)
- vesicles
- secretory granules
neurotransmitters stored in vesicles/secretory granules are released via ()
exocytosis
membrane proteins on vesicles and cell membrane; facilitate tight association between vesicle and target cell membrane
SNAREs
() binding to SNARE complex causes conformational change -> results in fusion of synaptic vesicle membrane and presynaptic terminal membrane
Ca2+
Vesicles are prepared by () mechanism
docking and priming
Vesicle components fused to cell membrane are recycled via ()
endocytosis
2 major kinds of NT receptors:
- ligand-gated channels (transmitter-gated)
- G protein-coupled receptors
summarize the mechanism of G protein-coupled receptors
G protein subunits (intracellular messengers) are activated by binding to receptor; these subunits activate other molecules/channels to induce changes in cell
transmitter-gated ion channels are not that selective for ()
specific ions
ACh-gated ion channel: permeable to both ()
Na+ and K+
The critical value of Vm at which the direction of current flow reverses (in I-V plot): ()
reversal potential
(): transient postsynaptic membrane depolarization caused by presynaptic release of neurotransmitter
EPSP (excitatory postsynaptic potential)
EPSPs usually occur at () ion channels
ACh and Glu-gated
(): transient hyperpolarization of postsynaptic membrane potential caused by presynaptic release of neurotransmitter
IPSP (inhibitory postsynaptic potential)
IPSPs usually occur at () ion channels
Glycin and GABA-gated (usually for Cl-)
If NTR is more permeable to negative ions, opening generates net (1) (influx of 2) -> membrane is (3) -> inhibitory PSP
- outward current
- negative ions
- hyperpolarized
G protein-coupled receptors are often referred to as ()
metabotropic receptors
Activated G protein subunits activate ()
effector proteins
effect of ACh in heart
ACh activation of GPCR results in hyperpolarization -> reduces rate at which cardiac muscle cells fire acton potential
effect of ACh in skeletal muscle
ACh receptor on skeletal muscle is a transmitter-gated ion channel that when activated results in depolarization -> APs are fired
Presynaptic receptors sensitive to the neurotransmitter released by the presynaptic terminal called (), which are typically GPCRs
autoreceptors
common effect of autoreceptor activation is ()
inhibition of neurotransmitter release or synthesis
(1): Neurotransmitter re-enters presynaptic axon terminal and astrocytes through (2)
- Reuptake
- transporter proteins
Too high conc. of neurotransmitter often induce ()
desensitization
Receptor (): inhibitors of neurotransmitter receptors
antagonists
example of ACh receptor antagonist
curare
Receptor (): mimic actions of naturally occurring neurotransmitters
agonists
example of receptor agonist
nicotine
(): root cause of neurological and psychiatric disorders
Defective neurotransmission
(): neurotoxin protein preventing ACh release at the neuromuscular junction
Botulinum toxin
botox cleaves (), preventing exocytosis of vesicles containing ACh
SNARE proteins
Process by which multiple synaptic potentials combine within one postsynaptic neuron
synaptic integration
EPSP: reflect the number of (1) and the number of (2)
- transmitter molecules in a single synaptic vesicle
- postsynaptic receptors available at the synapse
minimal value of EPSP is caused by the release of ()
a single synaptic vesicle
Number of released vesicles determines () of EPSP
amplitude
Some vesicles are released even without AP stimulation; spontaneous response is regarded as release of ()
single synaptic vesicle
(): a method of comparing the amplitudes of miniature and evoked PSPs, can be used to determine how many vesicles release NT during normal synaptic transmission.
Quantal analysis
EPSPs generated simultaneously at different sites
spatial summation
EPSPs generated at same synapse in rapid succession
Temporal summation
Allows for neurons to perform sophisticated computations
EPSP summation
Integration of EPSPs: EPSPs added together to produce significant ()
postsynaptic depolarization
Length constant lambda is proportional to ()
Rm/Ri
large dendrite/axon diameter -> (large/small) Ri
small
Rm is (large/small) if membrane has a lot of leaky channels
small
These dendrites don’t generate APs, but they amplify PSPs; allows the effects of the AP to be delivered to longer distances
excitable dendrites
EPSP contributes to the AP based on
- number of excitatory synapses
- distance between synapses and spike initiation zones
- properties of the dendritic membrane
examples of dendritic membrane properties that affect EPSP
number of channels, diameter, internal cystolic props, etc.
Action of ()—Take membrane potential away from action potential threshold; thus they exert powerful control over neuron output
inhibitory synapses
Synapse inhibits current flow from soma to axon hillock.
shunting inhibition
If the membrane potential was less negative than −65 mV (Ecl), activation of certain ion channels in inhibitory synapses cause (1) and (2)
- Cl- influx
- hyperpolarizing IPSP
No AP is generated bc effects of PSPs cancel each other out
EPSP-IPSP cancellation
() results from synaptic transmission that modifies effectiveness of EPSPs generated by other synapses with transmitter-gated ion channels
modulation
